Near-Field MIMO Wireless Test Systems, Structures, and Processes

ABSTRACT

Systems, processes, and structures allow enhanced near-field testing of the uplink and/or downlink performance of MIMO wireless devices (DUT), such as for any of product development, product verification, and/or production testing. Signal channels may preferably be emulated to test the performance of a device under test (DUT) over a range of simulated distances, within a near-field test environment. An enhanced process provides automated testing of a DUT over a wireless network, e.g. such as but not limited to a WLAN. The enhanced MIMO channel emulator may preferably be operated over a high dynamic range.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/647,250, filed Oct. 8, 2012, which isincorporated herein in its entirety by this reference thereto.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates generally to testing structures and processes forwireless or RF (radio frequency) communications systems. Moreparticularly, the invention relates to structures and processes thatprovide near-field testing of MIMO wireless devices and systems.

2. Description of the Background Art

Single-input single-output (SISO) wireless devices have been developedand implemented for many years, to transmit and/or receive desiredsignals to/from other elements, to provide wireless connectivity andcommunication between devices in a wireless network, such as in awireless PAN (personal area network), a wireless LAN (local areanetwork) a wireless WAN (wide area network), a cellular network, orvirtually any other radio network or system. Such SISO devices mayoperate over a wide variety of frequency bands, such as but not limitedto 2.4 GHz and 5.0 GHz bands. Test systems and standardized test modelshave also been developed and implemented over the years for SISOwireless devices.

However, the growing demand for increased bandwidth, i.e. requirementsfor increased data transfer, has driven the development ofmultiple-input multiple output (MIMO) devices.

While numerous systems and standardized models have been developed forthe testing of SISO devices, there are currently no standard systems andmodels to adequately test the performance of multiple-input multipleoutput (MIMO) devices.

It would therefore be advantageous to provide a system, structure andmethod that provide adequate performance testing for MIMO devices for avariety of operating conditions. Such a system and process wouldconstitute a major technological advance.

SUMMARY OF THE INVENTION

Systems, processes, and structures allow enhanced near-field testing ofthe uplink and/or downlink performance of MIMO wireless devices (DUT),such as for any of product development, product verification, and/orproduction testing. Channels may preferably be emulated to test theperformance of a device under test (DUT) over a range of distances,within a near-field test environment. An enhanced process providesautomated testing of a DUT over a wireless network, e.g. such as but notlimited to a WLAN. The enhanced MIMO near-field test structures,systems, and processes may preferably be operated over a high dynamicrange.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an exemplary SISO system;

FIG. 2 is a schematic view of an exemplary MIMO system;

FIG. 3 is a schematic view of an exemplary enhanced near-field MIMOwireless test system;

FIG. 4 is a schematic diagram of an exemplary RF attenuation unit for anear-Field MIMO wireless test system;

FIG. 5 is a detailed partial schematic diagram of one path within an RFattenuation unit, between an inlet port that is connectable to one orthe channel antenna, and an outlet port that is connectable to a GoldenUnit Under Test (GUT) module;

FIG. 6 is a schematic diagram of an exemplary calibration module for anear-field MIMO wireless test system;

FIG. 7 is a schematic diagram of an exemplary GUT module for anear-field MIMO wireless test system;

FIG. 8 is a flowchart of an exemplary process for emulating systemperformance;

FIG. 9 is a chart that shows throughput as a function of path loss for a2 GHz Channel 6 Uplink (with a station (STA)/Client);

FIG. 10 is a second chart that shows throughput as a function of pathloss for a 2 GHz Channel 6 Uplink (with a station (STA)/Client);

FIG. 11 is a chart of test data for an RF Automation System (RAS);

FIG. 12 is a chart of test data for a first QC unit;

FIG. 13 is a chart of test data for a second QC unit;

FIG. 14 is a chart that shows throughput as a function of path loss fora 2 GHz Channel 6 RAS and QC uplinks (with a station (STA)/Client);

FIG. 15 is a chart of test data for a RAS unit;

FIG. 16 is a chart of test data for a first QC unit;

FIG. 17 is a chart that shows throughput as a function of path loss for2 GHz Channel 6 RAS and QC downlinks (with a station (STA)/Client);

FIG. 18 is a chart that shows throughput as a function of path loss for2 GHz Channel 6 downlinks (with a station (STA)/Client);

FIG. 19 is a chart of test data for a Netgear access point (AP) router;

FIG. 20 is a chart of test data for a first access point (AP) QC unit;

FIG. 21 is a chart of test data for a second access point (AP) QC unit;and

FIG. 22 is a partial cutaway view of an exemplary enhanced MIMO testchamber.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a simplified schematic view of an exemplary single input,single output (SISO) system 10. A first device 12, e.g. a transmitter12, transmits a wireless signal 16 from an antenna 14. The wirelesssignal 16 is received at an antenna 18 associated with a second,receiving device 20, which processes the signal 16, such as using signalprocessing circuitry and a microprocessor. Both the transmitter 12 andthe receiver 16 in the SISO system 10 seen in FIG. 1 have a singleantenna 14,18, and operate to either send or receive a single signal 16.

In the exemplary SISO system 10 seen in FIG. 1, one or both of thedevices 12, 20 may moved in relation to the other device 20,12, suchthat the distance 22 between the antennas 14,18 may vary, such asbetween transmissions of wireless signals 16, and/or during atransmission of a wireless signal 16. While the distance 22 changes thetime of flight of the wireless signal, the second device 20 can stillreceive and process the signal 16, as long as the signal 16 is not lost,e.g. such as from but not limited to path loss, i.e. path attenuation.Path loss may occur from a wide variety of conditions, such as but notlimited to any of distance, reflection, refraction, diffraction, and/orabsorption.

The performance of different SISO devices has readily been performed formany years, such as during any of design, development and production.Such testing may readily be performed at any distance 22, e.g. at anyrange between near-field and far-field. As SISO devices 12,20 comprise asingle SISO channel 24, to send and/or receive a single wireless signal22, there is inherently no difference due to distance, other thangeneral signal attenuation.

In contrast to the SISO system 10 seen in FIG. 1, FIG. 2 is a simplifiedschematic view of an exemplary multiple-input multiple-output (MIMO)system 40. A first MIMO device 42 transmits a plurality of wirelesssignals 46, e.g. 46 a-46 d from respective antennas 44, e.g. 44 a-44 d.The wireless signals 46 e.g. 46 a-46 d are typically received at acorresponding plurality of antennas 48, e.g. 48 a-48 d, associated witha second MIMO device 50, which processes the signals 46 a-46 n, such asusing signal processing circuitry 64 and at least one microprocessor 60.Both MIMO devices 42,50 in the MIMO system 40 seen in FIG. 2 have aplurality of antennas 44,48, wherein the devices are configured to sendor receive a plurality of signals 46, e.g. 46 a-46 d.

In the exemplary MIMO system 40 seen in FIG. 2, one or both of thedevices 42,50 may be moved in relation to the other device 50,42, suchthat the distance 52, 52 a-52 d, between antennas 44,48 may vary, suchas between transmissions of wireless signals 46, and/or during atransmission of a wireless signal 46. While the distance 52 changes thetime of flight of the wireless signal 46, the receiving device 50 canstill receive and process the signals 46, e.g. 46 a-46 n, as long as thesignals 46 are not lost, e.g. such as from but not limited to path loss,i.e. path attenuation. Path loss may occur from a wide variety ofconditions, such as but not limited to any of distance, reflection,refraction, diffraction, and/or absorption.

In contrast to SISO devices, e.g. 12, 20, the performance of MIMOdevices, e.g. 42,50 is uniquely dependent on the simultaneoustransmission of a plurality of signals 46 over a plurality of MIMOchannels 54, e.g. 54 a-54 d, as well as on the distance 52, e.g. 52 a-52d. For example, in a simplified MIMO system having two channels 54 a and54 d, each device 42,50 comprises two radio channels 54 that areindependent of each other. However, at the receiving end, each antenna48 a and 48 d receives a composite signal 46 a and 46 d that includesthe data from both signals 46 a and 46 d, e.g. “Data A” from a firstsignal 46 a, and “Data B” from a second signal 46 d, is received and“Data A plus B” at antennas 48 a and 48 d. Therefore, the receiver 50 isrequired to process the signals 46 a and 46 d to split the data, basedon each corresponding channel 54 a and 54 d, to recapture the data, e.g.“Data A” at the first channel 54 a and “Data B” at a second channel 54d, and prevent interference between the channels 54 a and 54 d.

Since the plurality of signals 52 a and 52 d are transmittedsimultaneously in a MIMO system 40, the bandwidth is increased, e.g.such as to double the bandwidth as compared to an equivalent SISO system10. Similarly, the addition of more channels, e.g. Three by Three (3×3)or Four by Four (4×4) MIMO systems 40, provides increased bandwidth,along with further processing requirements to split the combined andsummed signals for the plurality of channels 54 a-54 d.

It is important to avoid interference and/or cancellation betweenchannels 54 a-54 d, since the signals 52 a-52 d typically have the samefrequency and amplitude. As well, since the receiving device, e.g. 50,receives each of the plurality of signals, e.g. 52 a and 52 d,simultaneously, the receiving device, e.g. 50 cannot identify whichsignal 52 is coming from which antenna 44, e.g. 44 a or 44 d.

Signal processing for the transmission and/or reception of MIMO signals52 is typically performed by one more processors 60, i.e. chipsets 60 inthe MIMO devices 42,50, wherein independent chipset vendors, commonlyprovide the chipsets, and all internal blocks.

FIG. 3 is a schematic view of an exemplary enhanced near-field MIMOwireless test system 100. A test chamber 102 comprises a first region104 a, a second region 104 b, and a third region 104 c. A device undertest (DUT) 106 is locatable within the first test region 104 a. Thefirst test region may preferably comprise RF shielding, e.g. such as butnot limited to any of double-walled steel, mesh, fabric, paint, and/orfoam.

The enhanced near-field MIMO wireless test system 100 provides astandard system and emulation model to adequately test the performanceof MIMO devices 106, both for near-field performance and far-fieldperformance. For example, in some embodiments 100, far-field performanceof a MIMO device 106 may preferably be emulated within a near-field MIMOtest system 100.

An antenna matrix 108 comprises a plurality of test antennas 110, e.g.110 a-110 d, which are located in and extend 118 from the first testchamber 104 a. The antenna matrix 108 is connected 118 to an RFattenuation unit 120. Furthermore, a reference antenna (REF) 112 islocated in and extends 116 from the first test region 104 a, and is thenconnected to meter 122 within the RF attenuation unit 120. In a currentsystem embodiment, the meter 122 comprises an RF & Microwave power meter122, which provides simultaneously scanning multichannel measurement,for self-calibration of the enhanced near-field MIMO wireless testsystem 100.

Each of the antennas 110, e.g. 110 a-110 d, in the antenna matrix 108preferably comprises a time division duplexing (TDD) antenna 110, whichapplies time-division multiplexing, e.g. such as to separate outward(uplink) signals 52 and return (downlink) signals 52.

For example, in a four-by-four setup, each DUT 106 comprises fourtime-division multiplexed (TDM) antennas 44, wherein each of the deviceantennas 44 a-44 d is configured to both transmit uplink signals 46 andreceive combined downlink signals 46. For such a four-by-fourconfiguration, to test the MIMO performance of the DUTs 106, each of thefour test antennas 110 a-110 d in the test system 100 is configured toboth receive combined uplink signals 46, and transmit downlink signals46, which are preferably attenuated and combined to simulate one or moredistances 52 between the test antennas 110 and the device antennas 44a-44 d. The test antennas 110 a-110 d comprise part of the test system100, and typically comprise standard MIMO antennas inside the DUT testregion 104 a.

The antenna matrix 108 provides input paths 118 (FIG. 5), e.g. fourpaths 118 a-118 d for a 4×4 DUT 106 and a 4×4 MIMO test system 100, thatare connected to a signal processing circuit 121, such as through ainput signal processing assembly 123, wherein the signal processingcircuit 121 comprises a programmable attenuator assembly 124.

The programmable attenuator assembly 124 typically comprises a pluralityof programmable attenuators, e.g. 124-124 d (FIG. 4, FIG. 5),corresponding to each of a plurality of antenna paths 118.

Each of the programmable attenuators 126 is configured to simulatereal-world distance for each of the plurality of antenna paths 118 a-118d. For example, on a current MIMO test system embodiment 100, theprogrammable attenuators 126 may preferably be configured any distancefrom Zero meters to one or more kilometers.

The programmable attenuator 124 is connected to at least one Butlermatrix 126, which is configured to combine the plurality of MIMOsignals, to emulate one or more real-world conditions, e.g. emulatingthe combined MIMO signal for a plurality of distances. In some systemembodiments 100, the system 100 is configured to provide selectableswitching between Butler matrix blocks 126, such as between a 2.4gigahertz block 126 a (FIG. 4, FIG. 5) and a 5 gigahertz block 126 b(FIG. 4, FIG. 5).

The system 100 is therefore preferably configured to adjust theattenuation, which simulates the distance 52, e.g. 52 a,52 b, betweenthe device under test 106 and the test antennas 110. The attenuation maypreferably be programmed digitally, and may preferably be varied, suchas independently or in tandem.

The output of the Butler matrix assembly 126 is connected, such asthrough an output signal processing assembly 130, to an output port 236(FIG. 4), which is connectable 150,146 to a calibration module 138, orto a GUT module 140, such as located within the third test region 14 c.

A signal source 136, such as located in the RF attenuation unit 120, isalso connectable 137 to the calibration module 138. In some currentsystem embodiments 10, the signal source 136 comprises a Lab Brick LSGSeries Signal Generator, e.g. Model LSG-02, available through VaunixTechnology Corporation, of Haverhill, Mass., having a frequency rangefrom 20 MHz to 6 GHz. For calibration, the signal source 136 isconfigured to generate a continuous-wave (CW) signal at desiredfrequency, which is pumped into the antenna matrix 118, i.e. the antennachain 118, and then matched using the power meters 192, 122.

The exemplary test system 100 seen in FIG. 3 comprises a 4×4 QC teststation 100, for testing the near field performance of a 4 channel MIMOdevice 106. The enhanced system 100 and associated process 340 (FIG. 8)provides testing, within a small, i.e. near-field, form factor, whileemulating a significantly larger, i.e. far-field, environment, whereinthe system 100 accurately determines the performance of a DUT 106 in areal-world MIMO environment.

In the exemplary test system 100 seen in FIG. 3, one or more of thecables between components, e.g. 116,118, 137, 146, etc. may preferablycomprise coaxial RF coaxial cables, with suitable connectors, such asbut not limited to SubMiniature version A (SMA) connectors. Otherelectrical connections, such as but not limited to signal connectionsbetween components located within the third region 14 c of the testchamber 102, may comprise RJ45 wiring and connectors.

FIG. 4 is a schematic diagram 180 of an exemplary RF attenuation unit120, such as for a near-field MIMO wireless test system 100. Theexemplary RF attenuation unit 120 seen in FIG. 4 is mounted within anenclosure 181. FIG. 5 is a detailed partial schematic diagram 240 of onepath 118 within an RF attenuation unit 120, between an inlet port 183that is connectable to the antenna matrix 108, and an outlet port 236that is connectable to the calibration module 138 and the GUT module140.

As seen in FIG. 4, an input of the signal source 136 is connected 188 toa USB port 190. The output of the signal source 136 is connected to anRF amplifier 182, which feeds into a PS element 184. In a currentexemplary system 100, the RF amplifier 182 comprises a wide band poweramplifier 182. The PS element 184 is then connected to an output 186,which is connectable 137 to the calibration module 138 (FIG. 2,FIG. 6).The PS element 184 is also connected to a power meter 192, which isconnected 194 to a corresponding USB port 196.

As also seen in FIG. 4, the reference antenna cable 116 is connectableto a reference input port 198, which is connected to a reference signalpower meter 122. The reference signal power meter 122 is also connected200 to a corresponding USB port 202. In a current system embodiment, thepower meters 122 and 192 comprise RF & Microwave power meters.

The exemplary signal processing circuit 121 seen in FIG. 4 and FIG. 5comprises a input signal processing assembly 123 between the input port183 and the programmable attenuators 124. In some embodiments, the inputsignal processing assembly 123 comprises a Pad 242 and a DC block 244corresponding to each antenna 110, e.g. 110 a-110 d, of the test antennamatrix 108, which are connected to a corresponding attenuator module foreach signal path. In some current embodiments, the programmableattenuators 124, e.g. 124 a-124 d, comprise solid state programmableattenuators, such as Model No. 50P-1857, available from JFW Industries,Inc. of Indianapolis, Ind.

The exemplary signal processing circuit 121 seen in FIG. 4 and FIG. 5also comprises a post attenuation processing assembly 125 between theprogrammable attenuation elements 124, e.g. 124 a, and one or morecorresponding butler matrix modules 126. In some embodiments, the postattenuation processing assembly 125 comprises a DC block 246, a Pad 248,and eight RF switch elements 250. In some current embodiments, the RFswitch elements 250 comprise single pole multiple throw (SPnT) RFswitches.

As seen in FIG. 4 and FIG. 5, the each signal path 240 in a signalprocessing circuit 121 may comprise one or more Butler matrix modules126, e.g. 126 a,126 b. For example, a first Butler matrix module 126 aseen in FIG. 5 comprises a 4×4 module for 2G operations. In an exemplarycurrent embodiment, the first Butler matrix module 126 a comprises aModel BC44-30 module, available through Emhiser Tele-Tech, Incorporated,of Belgrade, Mont. As well, the second Butler matrix module 126 b seenin FIG. 5 may preferably comprise a 4×4 module for 5G operation, whichin one current embodiment comprises a Model BC44-31 module, alsoavailable through Emhiser Tele-Tech, Incorporated. In addition, thesignal processing circuit 121 may further comprise an RF attenuation padelement 252 and/or a matrix bypass connection 253.

The exemplary signal processing circuit 121 seen in FIG. 4 and FIG. 5also comprises an output signal processing assembly 130 between theButler Matrix assembly 126 and the output port 236, such as comprisingbut not limited to eight RF switch elements 254, a Pad element 256, anda PS element 258. In some current embodiments, the RF switch elements254 comprise single pole multiple throw (SPnT) RF switches. The Padelement 256 typically comprises an RF attenuation pad, such as to reducethe level of the output signal to an acceptable level for input to anyof the calibration module 138 or the GUT module 140.

The RF switch elements 250 and 254 allow the exemplary 100 embodimentseen in FIG. 4 and FIG. 5 to be controllably switched between modules inthe Butler Matrix Assembly 126, e.g. between any of the first Butlermatrix module 126 a, the second Butler matrix module 126 b, the RFattenuation pad element 252, or the matrix bypass connection 253, foreach of the antenna paths 118.

As further seen in FIG. 4, the RF attenuation module 120 furthercomprises a control board 230, having one or more power inputs 232, e.g.a 5 volt DC supply 232 a, a 24 volt DC supply 232 b, and/or a 12 volt DCsupply 232 c. The control board 230 controls several modules within theRF attenuation module 124, such as comprising any of the relays, theattenuators 124, and any switching that is required between componentsand paths 118.

In some system embodiments 100, the control board 230 is configured toprovide selectable switching between Butler matrix blocks 126, such asbetween a 2.4 gigahertz block 126 a (FIG. 4, FIG. 5) and a 5 gigahertzblock 126 b (FIG. 4, FIG. 5). As well, the control board 230 maypreferably be configured to provide simultaneous operation at aplurality of frequencies, e.g. simultaneous 2.4 gigahertz and 5gigahertz operation.

FIG. 6 is a schematic diagram 280 of an exemplary calibration module 138for a near-field MIMO wireless test system 100, which typicallycomprises a metal enclosure 282. A 4-Way power divider 284, i.e. a powercomb 284, is mounted within the enclosure 282, and is connected 137 tothe signal source 136 at the attenuation module 124. In an exemplarycurrent system embodiment 100, the 4-Way Power Divider 284 comprises anRF power divider/combiner, which is rated at a frequency range of 2 GHzto 8 GHz. Outputs 286, e.g. 286 a-286 d for a 4×4 system 100, extendfrom the power divider 284 to corresponding splitter/combiner modules288, e.g. 288 a-288 d. In a current system embodiment 100, thesplitter/combiner modules 288 a-288 d comprise RF powerdivider/combiners.

The calibration module 138 allows automated calibration for the enhancedtest system 100, using a known sample signal from the frequency source136. The known signal is transmitted 146,150 into all four paths 118,e.g. 118 a-118 d, via the power comb 284 and splitter/combiners 288. TheRF switches 250 and 254 (FIG. 5) are then controlled, to deactivate orturn off all but one of the paths 118. For example, three paths 118b-118 d are turned “OFF”, to terminate the corresponding signals, whilethe remaining path 118 a is turned “ON”. The chosen “ON” path 118, e.g.118 a, carries the signal from the frequency source 136, through theswitches 250, the butler matrix 126, the pads 248, the correspondingattenuator 124, e.g. 124 a, and up to the corresponding antenna 110,e.g. 110 a, in the test chamber 104 a.

Using the power meter 192 (FIG. 4), the signal is measured at the sourcegoing into 137 the calibration module 138. Using the same power meter192, or a second power meter 22, the signal is measured at the referenceantenna 112 in the test chamber 104 a. These two measurements, whenadded, supply the path loss for the tested path 118, e.g. 118 a. As thesignal is known, the sent and received signal may be compared to theoriginal signal, which is used as a reference.

The same process is repeated for each of the other three paths 118, e.g.118 b-118 d, by varying the frequency source 136 to the desired channelfrequency, and selecting the path 118 to be calibrated.

FIG. 7 is a schematic diagram of an exemplary GUT module for anear-field MIMO wireless test system 100, which comprises a metalenclosure 302 having an interior region 304 defined therein. A goldenunit under test (GUT) 306 comprises a wireless MIMO device 306 that isknown to meet all required performance parameters, which can thereforeprovide a throughput mask, comprising the minimum allowed throughput inMbps at each attenuation or range level, by which to compare theperformance of a device under test 106.

As seen in FIG. 7, a golden unit under test (GUT) 306 is located withinthe interior region 304 of the GUT module enclosure. Signal cables 308are connected to the GUT 306, such as to connect 146, e.g. through 8 SMAconnectors 146, to the RF attenuation unit 120. In some embodiments, thesignal cables 308 comprise RF cables 308, e.g. RF interface cables.Other connections are also made to the GUT device 306, such as a powerconnection 310, e.g. 12 volts DC, an RJ45 connector 312, and a USBconnection 314.

The enhanced MIMO test system 100 may be configured in a wide variety ofsizes, such as for but not limited to testing 3×3 and/or 4×4 MIMOdevices 106. For example, an enhanced MIMO test system 100 that isconfigured to design and/or development may have a relatively largefirst region 104 a, such as having a volume of about 27 cubic meters,e.g. having 3 meter sides. The enhanced MIMO test system 100 can readilyemulate a real-world environment, and can also compensate fordifferences within the test environment. Therefore, for productiontesting, the enhanced MIMO test system 100 may readily be configuredwith a smaller, i.e. near-field, form factor, such as to decrease thecost and/or complexity of the chamber.

Each of the embodiments of the enhanced MIMO test system 100 provideadequate multipart capabilities, within a physical environment havingreduced interference, to maximize the performance validation for devicesunder test 106.

FIG. 8 is a flowchart of an exemplary process 340 for emulating systemperformance of a device under test DUT 106. At step 342, an enhancedMIMO test system 100 is provided, which is configured to emulate any ofthe uplink or downlink operation of the DUT 106 over a plurality ofdistances, e.g. from near-field to far-field.

At step 344, a MIMO device to be tested DUT 106 is placed within thefirst region 104 a of the test chamber 102, and is connected to a powersupply and other leads, e.g. such as but not limited to test signalinputs, and/or signal outputs. One or more operation modes of the DUTand/or the system 100, may be set at step 346, such as based upon afrequency mode, an emulated distance, or other operation modes.

At step 350, the system 100 determines if the measured performance ofthe DUT 106 is acceptable for the tested mode, e.g. such as by measuringpath loss 402 (FIG. 9) and throughput 404 (FIG. 9) of the DUT 106. Ifthe performance determination 350 is negative 352 for the tested mode346, such as if the measured performance does not meet pass-failcriteria, the system 100 may provide an output 354 to indicate thefailure, such as but not limited to a printed output, a displayedoutput, a light, a sound, or other indication.

In some system embodiments 100, such as for prototyping and/or productdevelopment or troubleshooting, it may be desirable for a device 106that fails one test 348 to continue 355 to be tested for other modes, orto be modified or repaired and retested. In production, further testingmay cease if a DUT 106 fails any test, wherein the unit may be any ofdiverted, tagged, or rejected.

If the performance determination 350 is positive 356 for the tested mode346, such as if the measured performance meets pass-fail criteria, adetermination 358 may be made whether there are any more remaining testsor modes that need to be performed on the DUT 106. If so 360, theprocess 340 may preferably return 362, e.g. such as to select 346 andtest 348 another mode. If all tests are completed 364, the system 100may provide an output 366 to indicate the success, such as but notlimited to a printed output, a displayed output, a light, a sound, orother indication.

FIG. 9 is a chart 400 that shows a comparison between throughput 404 asa function of path loss 402 for a first exemplary device under test 106a, as compared to expected performance data, wherein the first exemplarydevice under test 106 a comprises an N750 wireless dual band Gigabitrouter access point (AP), available through Netgear Inc., of San Jose,Calif., which is configured to run both 2.4 GHz and 5 GHz bandsconcurrently. The first plot 406 in FIG. 9 shows the expected Uplinkthroughput 404, in Mb/s) as a function of path loss 402 (in dB) for anRAS reference device, e.g. a GUT 306, or data. The second plot 408 a inFIG. 9 shows the uplink throughput 404, in (Mb/s) as a function of pathloss 402 (in dB) for a device under test 106, such as for qualitycontrol (QC) testing that may preferably be performed at a productionlocation.

FIG. 10 is a second chart 440 that shows a comparison between throughput404 as a function of path loss 402 for a second exemplary device undertest 106 b, as compared to expected performance data, wherein the secondexemplary device under test 106 b also comprises a Netgear N750 wirelessdual band Gigabit router. The first plot 406 in FIG. 10 shows theexpected Uplink throughput 404, (in Mb/s) as a function of path loss 402(in dB) for the RAS reference device, e.g. a GUT 306, or data, such asalso shown in FIG. 9. The second plot 408 b in FIG. 10 shows the uplinkthroughput 404, (in Mb/s) as a function of path loss 402 (in dB) for asecond device under test 106, such as for quality control (QC) testing.

As seen in FIG. 9 and FIG. 10, the resultant performance betweencomparable devices under test 106 yields test data that can be comparedto the reference data 406, to determine which devices under test 106meet, or fail to meet, a threshold level of performance. FIG. 11 is achart 460 of test data for an RF Automation System (RAS), e.g. a GUT306. FIG. 12 is a chart 480 of test data for the first device under test106 a, such as for quality control (QC) testing. FIG. 13 is a chart 500of test data for the second device under test 106 a, such as for qualitycontrol (QC) testing. In some system embodiments, any of the plots 406,408 or the data may be provided, such as for any of output, storage, ordisplay. As discussed, above, an automated result, e.g. pass or fail,may be provided based on the results of one or more test.

FIG. 14 is a chart 520 that shows a comparison between throughput 404 asa function of path loss 402 for a third exemplary device under test 106,e.g. 106 c, as compared to expected performance data, wherein the secondexemplary device under test 106 c also comprises a Netgear N750 wirelessdual band Gigabit router. The first plot 406 in FIG. 14 shows the Uplinkthroughput 404, (in Mb/s) as a function of path loss 402 (in dB) for theRAS reference device, e.g. a GUT 306, or data. The second plot 408 c inFIG. 14 shows the uplink throughput 404, (in Mb/s) as a function of pathloss 402 (in dB) for a third device under test 106, e.g. 106 c, such asfor quality control (QC) testing. FIG. 15 is a chart 540 of test datafor an RAS reference device, e.g. a GUT 306. FIG. 16 is a chart 560 oftest data for the third device under test 106 c, such as for qualitycontrol (QC) testing.

FIG. 17 is a chart 600 that shows a comparison between downlinkthroughput 604 as a function of path loss 602 for an exemplary deviceunder test 106 d, as compared to expected performance data, wherein theexemplary device under test 106 d comprises an N900 wireless Dual BandGigabit router access point (AP), available through Netgear Inc., of SanJose, Calif., which is configured provide up to 900 Mbps of combinedthroughput (rated at 450 Mbps for each channel). The first plot 606 inFIG. 17 shows the expected downlink throughput 604, in Mb/s) as afunction of path loss 602 (in dB) for an RAS reference device, e.g. aGUT 306, or data. The second plot 608 a in FIG. 17 shows the downlinkthroughput 604, in (Mb/s) as a function of path loss 602 (in dB) for anexemplary device under test 106 d, such as for quality control (QC)testing, which may preferably be performed at a production location.

FIG. 18 is a chart 640 that shows a comparison between downlinkthroughput 4604 as a function of path loss 4602 for an alternateexemplary device under test 106 e, as compared to expected performancedata, wherein the second exemplary device under test 106 e alsocomprises a Netgear N900 wireless dual band Gigabit router. The firstplot 606 in FIG. 18 shows the expected downlink throughput 604, (inMb/s) as a function of path loss 602 (in dB) for the RAS referencedevice, e.g. a GUT 306, or data, such as also shown in FIG. 17. Thesecond plot 608 b in FIG. 18 shows the downlink throughput 604, (inMb/s) as a function of path loss 602 (in dB) for the alternate exemplarydevice under test 106 e, such as for quality control (QC) testing.

As seen in FIG. 17 and FIG. 18, the resultant downlink performancebetween comparable devices under test 106 d,106 e yields test data 608a,608 b that can be compared to the reference data 606, to determinewhich devices under test 106 meet, or fail to meet, a threshold level ofperformance.

FIG. 19 is a chart 700 of test data for a Netgear N900 wireless dualband Gigabit router RAS reference device, e.g. a GUT 306. FIG. 20 is achart 720 of test data for a first Netgear N900 wireless dual bandGigabit router, such as for quality control (QC) testing. FIG. 21 is achart 740 of test data for a second Netgear N900 wireless dual bandGigabit router, such as for quality control (QC) testing. In some systemembodiments, any of the plots 606, 608 or the data may be provided, suchas for any of output, storage, or display. For example, as seen in FIG.18, the second Netgear N900 wireless dual band Gigabit router DUT 106 eprovides near-field and far-field downlink performance 608 b, asemulated in the enhanced test system 100, that may is relativelyconsistent with the reference data 606. In contrast, the first DUT 106 dprovides near-field and far-field downlink performance 608 a, asemulated in the enhanced test system 100, which indicates a drop inthroughput 604 at higher levels of path loss, as compared with thereference data 606. As discussed, above, an automated result, e.g. passor fail, may be provided based on the results of one or more tests.

The enhanced near-field MIMO wireless test system 100 may be embodiedwithin a relatively small form factor, which is configured to test awide variety of MIMO devices up to their maximum bandwidth, for each ofa plurality of radio channels 54 a-54 d, for downlink and/or uplinkoperation. The operation of the channels may preferably besimultaneously excited, such that each of the transmitted signal arereceived properly on their destination.

The enhanced near-field MIMO wireless test system 100 is configured tooperate in a near-field test environment, while emulating performanceand/or providing correlation to provide results that reflect theperformance of devices under test (DUT) 106 under real-world conditions.The enhanced system 100 and process 340 therefore provides testing,within a small, i.e. near-field, form factor, while emulating asignificantly larger, i.e. far-field, environment, wherein the systemaccurately determines the performance of a DUT in a real-world MIMOenvironment.

The enhanced near-field MIMO wireless test system 100 may preferably beconfigured to provide near-field testing for any of:

-   -   product development;    -   product validation; and/or    -   product production and shipping, e.g. quality control.

As well, the relative form factor, i.e. size, of the near-field MIMOwireless test system 100 may suitably be adapted for the type of testingto be performed. For example, product development testing may preferablybe performed in a larger test chamber, such as for but not limited to:

-   -   larger test antennas 110;    -   room for different or additional instrumentation and/or sensors;    -   room for engineers and/or technicians;    -   room for larger prototypes; and/or    -   increased access to any of DUTs 106, antennas, 110, 122, cables,        or connections.

Testing of MIMO devices for product production and shipping maypreferably be performed at one or more facilities, such as associatedwith one or more original device manufacturers (ODMs), e.g. contractmanufacturers, and/or chipset vendors. The relative form factor, i.e.size, of the near-field MIMO wireless test system 100 is readilyadaptable to the testing of DUTs 106 in production environments, such asat an ODM facility, wherein the space, cost and speed of testing becomesincreasingly important. In such a testing environment, a small scaletest chamber 102 may be used, having a relatively small DUT region 104a, wherein the near-field MIMO wireless test system 100 may readilyprovide performance testing over the full bandwidth of the DUTs 106,using signal emulation and data correlation to accurately reflect thedownlink and/or uplink performance of DUTs 106 for different levels ofpath loss 402,602, i.e. reflecting DUT performance at differentdistances 52.

For a particular group of DUTs 106, near-scale MIMO performance trackingmay preferably be performed using different test chambers 10, such aswithin both a larger near-scale chamber 102 and a smaller near-scalechamber 102, wherein the performance results may be compared between thedifferent chambers 102. For example, the performance, of a known deviceunder test DUT 106 may be compared to the performance of the same deviceDUT 106 within a different chamber 102, such as to confirm thesuitability of a new near-scale chamber 102 for subsequent testing 340.In some embodiments, comparisons may preferably be made between one ormore data points, and/or between entire performance charts, e.g. 408,608.

In another example the performance of one or more wireless MIMO DUTs106, such as representative of a new MIMO product series, may be testedwithin a first, i.e. known and trusted, larger near-scale chamber 102,such as to establish baseline specifications for the product series,along with establishing acceptable tolerances for the uplink and/ordownlink throughput 204,404 at different levels of path loss 402,602,wherein the path loss is correlated to the attenuation of the device atdifferent distances, i.e. ranges.

Thereafter, quality control testing 340 may be performed at any of thesame test system 100, or at a different test system 100, such asconfigured for time and cost-efficient production testing, wherein theperformance of production DUTs is checked and compared 350 (FIG. 8) toone or more of the previously established values and tolerances.

Therefore, during product development, wireless MIMO devices mayinitially be tested within a full scale chamber. At a latter stage indevelopment, or in a latter stage, i.e. mass production, testing may beperformed in the enhanced, i.e. small scale, test system 100, whichprovides improved setup, and decreased time and cost for quality controltesting.

FIG. 22 is a partial cutaway view 800 of an exemplary test chamber 102for an enhanced MIMO test chamber 100. In some embodiments of the testchamber 102, the any of the DUT 106 or the matrix 108 of antennas 110,e.g. 110 a-110 d, are moveable 804 in relation to each other. Forexample, as seen in FIG. 22, a movement mechanism 806 may preferablyprovide controlled movement 804 of a device under test DUT 106 in one ormore directions 802, e.g. such as comprising movement 804 in anX-direction 802 x, in a Y-direction 802 y, and/or in a Z-direction 802z.

The matrix 108 of antennas 110, e.g. 110 a-110 d, seen in FIG. 22 maypreferably be specified based on type of testing preformed with thespecific MIMO test system 100. For example, in a large scale system 100that is configured for initial product development, the antennas 110 maybe chosen with less constraints on size and/or cost, while having moreconstraints on desired accuracy and/or sensitivity. In a current systemconfigured for such testing, the test antennas cost approximately$10,000 each. In contrast, for a smaller scale system that is configuredfor latter quality control, the antennas 110 may be chosen with moreconstraints on size and/or cost. In a current system configured for suchquality control testing, the test antennas cost approximately $100 each.While some components may be chosen to reduce the cost of some enhancedtest systems 100, such as for production testing that requires basicconfirmation of performance throughput at a limited number ofattenuation levels, other parts and components, such as but not limitedto any of standard parts, cables, instrumentation, processors,controllers, or storage.

As seen in FIG. 22, the matrix 108 of test antennas 110 a-110 dcomprises part of the enhanced MIMO test system 100, and typicallycomprises standard MIMO antennas inside the DUT test region 104 a. Theantenna connections 118 (FIG. 18, typically comprise cables, e.g. SMAcables, that extend from the DUT test region, such as directly, orthrough fittings, e.g. coaxial bulkhead fittings, which are connectableto one or more cable connections that extend, such as through aconnection region 104, toward the RF attenuation unit 120.

Similarly, devices to be tested DUT 106 are connectable, such as throughfittings in the DUT test region, for any of power, as well as for inputand output signal connections 134 (FIG. 3). During testing, one or moreinput signals 134, such as from a controller 132 (FIG. 3) are sent tothe DUT, for the testing of processing and uplink performance.Similarly, received MIMO wireless MIMO downlink signals are received andprocessed by the DUT, wherein the resultant downlink signal 134 istransferred 134 and analyzed during the testing process.

As also seen in the FIG. 22, the matrix 108 of test antennas 110, e.g.110 a-110 d, may preferably be located closely with respect to eachother, such as having a consistent spacing 812 between them. In onecurrent system embodiment 100, the antenna spacing 812 is 1 cm, whichallows the antennas 110 to operate in a near-field environment 104 a,while emulating any desired range in free space, from near-field to longrange.

As further seen in FIG. 22, the DUT test region 104 a may preferablycomprises absorbing elements 810, such as to significantly reduce oreliminate reflected RF signals, such as located on all the interiorsurfaces of the DUT region 104, e.g. top, bottom, sides, and access door814.

Once the DUT 106 is placed within the DUT test region and connected topower and signal connections 134, the access door is closed, and thesystem 100 powers up the DUT 106, to exercise and test the DUT 106 forall tested parameters and/or modes.

While the exemplary DUT test region 104 a shown in FIG. 22, comprises adoor 814, it should be understood that access 814 for the DUT testregion may preferably be located anywhere with respect to the innerregion 104 a. For example, in some system configurations 100 that areconfigured for production testing 340, access 814 may be located on thetop of the DUT region 104 a, wherein a DUT 106 to be tested is loweredinto the DUT region 104 a, such as onto a test jig that comprises quickconnections for power, input, and output signal signals, e.g. an RJ45connector. In such as configuration, once the DUT 106 is hooked up andpowered, the access door 814 is closed, and testing can begin.

As seen in FIG. 3 and FIG. 22, the a large portion of the controls,hardware and connections associated with the multiple inputs and outputs(MIMO) may preferably be located away from the DUT region 104, such aswithin any of the intermediate region 104 b and/or the backend controlregion 104 c. For example, the back end of the test antenna matrix 108,and the antenna cable 118 may preferably be routed through theintermediate region, such as exiting the chamber through a side panelbulkhead 114. The transmission and reception of wireless signals isintermingled, such in compliance with the real-world operation of theTDM device under test 106, to perform the near-field MIMO testing 340that properly reflects how the device 106 is required to operate. Thedesign of the test structure and methods for MIMO testing is readilyscalable for the different system embodiments 100, even within a smallform factor that may be required for production testing.

The enhanced near-field MIMO wireless test system 100 is thereforeconfigurable to perform both uplink and downlink testing, to simulatemultipath operation at different distances, for a plurality of modesand/or steps, such as to determine the throughput (megabits per second)of a device under test 106, as a function of path loss (dB).

In some system embodiments 100, such as for product development, testing340 may be performed over a wide range of uplink and/or downlink pathloss 402,602, such all the way to the point where the throughput 404,604becomes zero. In other system embodiments 100, such as for productionquality control, testing 340 may be performed over a certain range, suchas to confirm that the performance is consistent with expected pass-failcriteria within part of the range, and possibly to confirm where thethroughput starts dropping off at a certain angle. Such testing may notrequire testing the far range, i.e. all the way to the point where thethroughput 404,604 becomes zero, as such testing may take too much timeand fail to yield usable information for a production environment.

While some of the enhanced MIMO wireless test systems 100 are describedherein for Near-field testing of MIMO devices, it should be understoodthat many of the structures and processes may preferably be used forfar-field testing of components, such as for testing antennas. Forexample, the enhanced wireless test system 100 may preferably beconfigured to provide far-field measurements, such as for passiveantenna testing. Such a system 100 may preferably provide 2-dimensionalplots, simulated performance, and/or elevations, such as to gainspectral efficiency from one or more antennas.

Although the invention is described herein with reference to thepreferred embodiment, one skilled in the art will readily appreciatethat other applications may be substituted for those set forth hereinwithout departing from the spirit and scope of the present invention.Accordingly, the invention should only be limited by the Claims includedbelow.

1. A system comprising: a test chamber having an interior region definedtherein for mounting a MIMO device, the test chamber including at leastone power connection and at least one signal connection for the MIMOdevice; an antenna matrix located within the test chamber that includesa plurality of test antennas, where each of the test antennascorresponds to a MIMO channel; and an attenuation unit connected to theantenna matrix that includes a plurality of signal processing paths thatare controllable to emulate a plurality of distances between the MIMOdevice and the plurality of test antennas; and a controller configuredto control the attenuation of each of the plurality of signal processingpaths.
 2. The system of claim 1, where each of the signal processingpaths includes a programmable attenuator and a Butler matrix.
 3. Thesystem of claim 2, where the controller is configured to control each ofthe Butler matrices to controllable combine a signal.
 4. The system ofclaim 1, where the attenuation unit is switchable between a plurality offrequency modes.
 5. The system of claim 1, where the attenuation unit isconfigured to operate simultaneously on a plurality of frequency modes.6. The system of claim 1, further comprising: a signal source configuredto generate a calibration signal at a particular frequency; acalibration module configured to input the calibration signal into theantenna matrix; and a power meter configured to measure the calibrationsignal and a signal received by the antenna matrix.
 7. The system ofclaim 6, where the calibration signal is a continuous wave signal at theparticular frequency that is matched to the signal received by theantenna matrix using the power meter.
 8. The system of claim 1, wherethe interior region of the test chamber is composed of an RF shieldedregion that houses the MIMO device and the antenna matrix and at leastone other region.
 9. The system of claim 1, where the MIMO deviceincludes a plurality of device antennas that are configured to transmituplink signals and receive combined downlink signals.
 10. A methodcomprising: powering a MIMO device located within a test chamber;controllably processing a multipath signal through a plurality of signalpaths, wherein the multipath signal is attenuated to emulate a distancebetween the MIMO device and a plurality of test antennas, and whereineach of the plurality of test antennas is associated with an antennapath; transmitting the processed multipath signal from the plurality oftest antennas located within the test chamber; receiving, at each MIMOantenna of the MIMO device, a downlink signal corresponding to thetransmitted multipath signal; processing the downlink signals receivedby the MIMO device; and generating an output that characterizes downlinkperformance of the MIMO device based on the downlink signals.
 11. Themethod of claim 10, further comprising: outputting one or more of thedownlink signals received by the MIMO device.
 12. The method of claim10, further comprising: determining whether downlink performance of theMIMO device at a particular distance is within an acceptable level byanalyzing the downlink signals; and generating a performance indicatorthat specifies whether the MIMO device meets the acceptable level. 13.The method of claim 9, further comprising: determining throughput of theMIMO device at an emulated distance as a function of path loss; andcomparing the throughput to expected performance data for the emulateddistance.
 14. The method of claim 10, further comprising: controllingfrequency of each attenuated signal supplied by the plurality of signalpaths.
 15. The method of claim 10, further comprising: generating acalibration signal, wherein the calibration signal is a continuous wavesignal at a particular frequency; transmitting the calibration signalfrom the MIMO device; receiving the calibration signal at a referenceantenna; and measuring the calibration signal at the MIMO device and thereceived calibration signal at the reference antenna.
 16. The method ofclaim 10, further comprising: calculating path loss based on themeasured calibration signal and the received calibration signal.
 17. Themethod of claim 15, further comprising: comparing the measuredcalibration signal and the received calibration signal; and adjustingone or more of the antenna paths based on the comparison.
 18. A methodcomprising: causing an uplink signal to be transmitted by each of aplurality of device antennas of a wireless multiple input-multipleoutput (MIMO) device; receiving a combined signal at each of a pluralityof test antennas, where each test antenna is associated with an antennapath; attenuating each of the antenna paths with a programmableattenuator; combining the combined signals to emulate a distance betweenthe plurality of device antennas and the plurality of test antennas; anddetermining throughput of the MIMO device at the emulated distance. 19.The method of claim 18, further comprising: determining whether thethroughput of the MIMO device at the emulated distance is within anacceptable level; and generating a performance indicator that specifieswhether the MIMO device meets the acceptable level.
 20. The method ofclaim 18, where the MIMO device and the plurality of test antennas arelocated within an RF shielded region of a test chamber.